|  |  | Overview
Network administrators must figure out how to deny unwanted access to the network while allowing appropriate access. Although security tools, such as passwords, callback equipment, and physical security devices are helpful, they often lack the flexibility of basic traffic filtering and the specific controls most administrators prefer. For example, a network administrator might want to allow users access to the Internet, but might not want external users telnetting into the LAN. Routers provide basic traffic filtering capabilities, such as blocking Internet traffic, with access control lists (ACLs). An ACL is a sequential collection of permit or deny statements that apply to addresses or upper-layer protocols. In this chapter, you will learn about using standard and extended ACLs as a means to control network traffic and how ACLs are used as part of a security solution. In addition, this chapter includes tips, considerations, recommendations, and general guidelines on how to use ACLs, and includes the commands and configurations needed to create ACLs. Finally, this chapter provides examples of standard and extended ACLs and how to apply ACLs to router interfaces.
| Threaded Case Study
Washington School District Project: ACLs

In this chapter, you will learn the concepts and configuration commands that will help you use and implement ACLs in the Washington School District network. In addition, as ACL concepts and commands are introduced, you will be able to apply ACLs to your school site design and implementation.